In the forming of large-area, flat concrete ground slabs in building construction, it is common practice to place the pour in sections with the use of peripheral sheet metal screeds at the junctures between sections. Among the advantages of this procedure are that the heavy work of placement can proceed at a more leisurely pace, the screeding of relatively small areas produces a flatter slab, and the finished slab sections have a slight "float" with respect to one another at their screed junctures, thereby relieving stresses such as caused by temperature changes which might otherwise occur in a comparatively large monolithic slab pour. The sheet metal screeds used are assemblies of a screed member having a reversely-bent marginal upper end portion providing a longitudinally-extending recess open at the bottom, which is hookingly engaged over the upper end of a plurality of sheet metal stakes spaced therealong and which are set into the foundation ground at appropriate distances to maintain the upper end of the screed at the upper level of the slab to be poured.
One of the deficiencies of using sheet metal screed and stake assemblies as described above for forming large area slab sections, is that the slab section junctures along the embedded screeds are difficult to seal against water infiltration. Caulking, if applied along the line of juncture, necessarily projects above the surface of the slab, and is therefore readily destroyed if the slab is used without floor covering, such as in warehouses, for example.